Assays for determining analytes by a solid phase technique involve contact between a sample suspected of containing the analyte and a device having a binder material specific for the analyte supported on a porous membrane. The amount of analyte which becomes bound to the binder on the porous membrane is then detected with a tracer as a measure (quantitative or qualitative) of the analyte in the sample.
Many companies have introduced assay test kits to screen for Group A Streptococcus ("GAS") in the physician's office. Other companies have introduced assay kits for home use to detect pregnancy and kits to detect ovulation. Some of these assay kits are enzyme immunoassays where the formation of a colored species indicates the presence (or absence) of the analyte.
Other assay kits presently available are agglutination immunoassays, typically using latex or erythrocytes as supports. Many assays do not give a clear indication of assay test results and lead to questions about the reliability of the test results. Furthermore, in the case of agglutination assays, test results are difficult to read at low analyte concentrations and suffer sometimes from non-specific agglutination.
A problem with current assay device technology is the lack of built-in quality control testing in an assay device for the binding material used to specifically bind an analyte of interest. Normally, in order to confirm that the binding material in the assay device used in the test was operational for a particular analyte, repeat testing utilizing a control sample of the analyte is required. The control test in many cases is carried out on another device from the same batch of assay devices used for the original assay. This results in customer dissatisfaction due to the increased cost of using an additional assay device for quality control testing. Furthermore, since the control test is not performed on the assay device used in the original assay, it is not a direct binder control test for the assay device used in the original test, but rather one for the binder in a batch of test devices.
Efforts have been made to develop assays which incorporated controls into assay devices in order to confirm the operativeness of the assay device. A test card incorporating a calorimetric indicator to determine the presence of a minute amount of a specific substance in a liquid medium was disclosed in U.S. Pat. Nos. 5,240,844 and 4,900,633 both to Wie et al. The test card has a test area which incorporates a binding support (e.g. a bacterial binding substrate) having a dense application of antibodies for the particular substance being tested. The test card also incorporates a control area which is juxtaposed to the test area, the control area incorporates the same binding support and antibody as the test area.
The assay disclosed by Wie et al. consists of administering a sample of a specific substance, i.e. an antigen, being tested in a liquid medium to the test port of the device. Any antigen present in the sample will immediately become bound to the antibodies immobilized on the binding support. The next step is the application of an aqueous solution of enzyme labelled antigen at the test port which will bind to any available antibodies. The next step involves the administration of a solution which will displace the solution containing uncombined, enzyme labelled antigen in the test port. If all of the antibodies in the test port were saturated with antigen from the test substance then no color indication will be observed because no enzyme-linked antigen was able to bind to the antibodies in the test port. However, if no antigens were present in the test substance, complete color saturation will be observed.
In the control port the enzyme-labelled antigens will completely saturate the antibodies and thus full color development will result, indicating both the operativeness of the device and the maximum color definition which can be expected if no antigens are present in the test substance.
Another device with a control region was disclosed in U.S. Pat. No. 4,916,056 to Brown et al. The device is useful in solid phase binding assays to determine the presence or amount of an analyte in a test sample. A positive control area is formed by providing a substance such as the analyte of interest which is capable of binding the enzyme label or other signal response material within the device control area. The positive control area and the analyte binding area are preferably in an interactive configuration in which the positive control area interacts with the analyte binding area upon the occurrence of a positive test result to form a first representational symbol having a known meaning to the user, and the positive control area acts alone upon the occurrence of a negative test. The positive control area disclosed by Brown et al. is used to indicate the operativeness of the enzyme label or other signal response material used to indicate the presence of an analyte rather than the operativeness of the reagent used in the test area to bind a particular analyte of interest.
U.S. Pat. No. 5,073,340 to Covington et al. discloses a test device for use in determining analyte wherein a binder for an analyte (e.g., antibody) to be detected is supported on a porous membrane. The use of an analyte positive control or negative control is disclosed. The control area may be completely or partially overlapping with the test area or it may be a completely separate area of the support. The analyte control disclosed by Covington indicates to the user that the tracer used to detect the presence of the desired analyte in the device was active.
U.S. Pat. No. 5,132,085 to Pelanek discloses an assay device having a frame with three wells at the bottom of which there is a reaction surface comprising an appropriate membrane, the membrane is in turn in contact with a liquid-absorbing material underneath. Antibody-carrying beads are attached to the reaction surface in each of the wells. One well serves the function of a control well. When a test sample is run on the assay the antibody on the beads complexes with its antigen (if present), which in turn complexes with a conjugate antibody bearing an appropriate label, that is added later. In the control well, beads are deposited that can serve as negative and positive controls. The deposited control beads have the antibody-antigen complex, which insures that when a viable labeled conjugate reagent is properly added as part of the procedure that the positive control area should display a detectable symbol. Accordingly, Pelanek's quality control procedure is for the labeled conjugate reagent and not for the antibody used in the assay.
Assay devices to date that have built-in control tests are directed to the operativeness of the labeling material used to indicate the presence of a desired analyte. A need has existed for a flow-through assay device having a built-in control test in the assay device that indicates the operativeness of the binding material used in the assay to specifically bind an analyte in a test sample. Additionally, it is also desirable that such an assay device also incorporate a control test for any labeled material used to indicate the presence of an analyte in such an assay. The present invention fulfills these needs.